Namespace-based issue indexes synchronous addition

Summary

This issue is to add a migration(s) to create the following database index(es) synchronously after it has been created/destroyed on GitLab.com:

  • index_issues_on_namespace_id_created_at_id_state_id
  • index_issues_on_work_item_type_id_namespace_id_created_at_state
  • index_issues_on_namespace_id_relative_position_id_state_id
  • index_open_issues_on_namespace_id_confidential_author_id_id
  • index_closed_incidents_on_namespace_id_closed_at

The asynchronous index(es) was introduced in !188963 (merged).

Edited by Heinrich Lee Yu